Method and apparatus for reducing acidic contamination on a process wafer following an etching process

ABSTRACT

A method and system for reducing acidic contamination on a process wafer following a plasma etching process including; providing an ambient controlled heating chamber for accepting transfer of a process wafer under controlled ambient conditions; transferring the process wafer to the heating chamber under controlled ambient conditions following plasma etching of the process wafer; providing a heat exchange surface within the heating chamber for mounting the process wafer in heat exchange relationship thereto; mounting the process wafer on a heat exchange surface contained within the heating chamber; and, heating the process wafer to a temperature sufficient to vaporize an acidic residue thereon to form acidic vapors; and, removing the acidic vapors from the heating chamber.

FIELD OF THE INVENTION

This invention generally relates to shallow trench isolation (STI)etching apparatus and methods and more particularly to reducing acidcontaminated residue associated therewith.

BACKGROUND OF THE INVENTION

In the integrated circuit industry today, hundreds of thousands ofsemiconductor devices are built on a single chip. Every device on thechip must be electrically isolated to ensure that it operatesindependently without interfering with another. The art of isolatingsemiconductor devices has become an important aspect of modernmetal-oxide-semiconductor (MOS) and bipolar integrated circuittechnology for the separation of different devices or differentfunctional regions. With the high integration of the semiconductordevices, improper electrical isolation among devices will cause currentleakage, and the current leakage can consume a significant amount ofpower as well as compromise functionality. Among some examples ofreduced functionality include latch-up, which can damage the circuittemporarily or permanently, noise margin degradation, voltage shift andcross-talk.

Shallow trench isolation (STI), is the preferred electrical isolationtechnique especially for a semiconductor chip with high integration. Ingeneral, conventional methods of producing an STI feature includeforming a hard mask over the trench layer, patterning a photoresistetching mask over the hard mask, etching the hard mask through thephotoresist etching mask to form a patterned hard mask, and thereafteretching the trench layer to form the STI feature. Subsequently, thephotoresist etching mask is removed and the STI feature is back-filledwith a dielectric material.

Frequently STI features are etched with a sequential process flow, wherethe mask layers are etched in one chamber and the silicon trench isetched in another chamber. Etching is frequently performed by way of aplasma. Typically, in a plasma etching process an etchant source gassupplied to an etching chamber where the plasma is ignited to generateions from the etchant source gas. Ions are then accelerated towards theprocess wafer substrate, frequently by a voltage bias, where they removematerial (etch) from the process wafer. Various gas chemistries are usedto provide variable etching rates for different etching targetmaterials. Frequently used etchant sources include chloro andfluoro-hydrocarbons in addition to HBr to etch through for example, asilicon layer to form a shallow trench isolation feature. Anotheretchant chemistry, for etching through silicon, for example, includes aCl₂/O₂/HBr-based chemistry. During and after the etching process halogenspecies such as chlorine and bromine remain on the target surface where,for example, they are incorporated into the sidewalls and bottoms ofetched features as well as into overlying layers of photoresist. Sincehydrogen is also present in and around the halogen species, highlycorrosive acids may condense and form on the process wafer causingcorrosive damage. HBr, for instance, is a highly corrosive acid that isfrequently formed on the surface of the process wafer.

FIG. 1 shows a typical process chamber configuration used in STIetching. The typical process chamber, for example, includes severaldifferent etching chambers, 10, 12, 14, and 16, in addition to a waferorientation chamber 18, a cool down chamber 24 and loadlock chambers 20and 22. The robotic arm transfer mechanism is centrally located at 26.In a typical process in STI etching, as explained, several differentetching steps with different etching chemistries may be involved thushaving the process wafer transferred by robotic arm 26 between multipleetching chambers, for example 10, 12, 14, and 16. Following etching, theprocess wafer may be transferred by robotic arm 26 to cool down chamber24 to cool the process wafer prior to transfer to a loadlock chamber,for example, 20 or 22 where the chamber is pressurized to atmosphericpressure for unloading.

During this process, corrosive acids, such as HBr may condense onto theprocess wafer surface which also contains for example, loose particlesfrom the etching process. Further, during the pressurization process theparticles may become dislodged and adhere to the chamber walls androbotic arm thereby causing corrosive damage to the chamber and roboticarm as well as to the process wafer. As a result, over time, theloadlock chambers accumulate residual corrosive particles which cancause damage to process wafers as they are moved through the loadlockchamber thereby necessitating frequent equipment shutdown for cleaning.Another shortcoming of the prior art procedure and apparatus for STIetching may be potential adverse health consequences to equipmentoperators from an undesired buildup of such contamination.

There is therefore a need in the semiconductor processing art to developapparatus and methods whereby the level of acid (e.g., HBr) contaminatedparticles on process wafers and STI etching apparatus in an STI etchingprocedure is reduced thereby minimizing damage to both process wafersand STI etching apparatus as well as reducing the potential effect ofadverse health consequences.

It is therefore an object of the invention to provide a method andapparatus whereby the level of acid (e.g., HBr) contaminated particlesis reduced in an STI etching process while overcoming other shortcomingsand deficiencies in the prior art.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention provides a method and apparatus forreducing acidic contamination on a process wafer following a plasmaetching process.

In a first embodiment of the present invention, a method is provided forreducing acidic contamination on a process wafer following a plasmaetching process including providing an ambient controlled heatingchamber for accepting transfer of a process wafer under controlledambient conditions; transferring the process wafer to the heatingchamber under controlled ambient conditions following plasma etching ofthe process wafer; providing a heat exchange surface within the heatingchamber for mounting the process wafer in heat exchange relationshipthereto; mounting the process wafer on a heat exchange surface containedwithin the heating chamber; and, heating the process wafer to atemperature sufficient to vaporize an acidic residue thereon to formacidic vapors; and, removing the acidic vapors from the heating chamber.

In another embodiment, the step of removing the acidic vapors is carriedcut simultaneously with the step of heating the process wafer. Inanother related embodiment, the steps of heating the process wafer andremoving the acidic vapor are carried out for a period of timesufficient to remove from about 50 percent to about 100 percent of theacidic residue. In yet another related embodiment, the step oftransferring the process wafer to the heating chamber is carried outprior to transferring the process wafer to an unloading chamber forunloading the process wafer.

In yet further related embodiments, the process wafer is heated within atemperature range of about 75° C. to about 100° C. Further, the ambientpressure within the heating chamber is maintained within a range of 10milliTorr to 500 milliTorr. Yet further, the step of heating the processwafer is carried out for a period of about 30 to about 90 seconds.

In further related embodiments, the heat exchange surface is suppliedwith a heat exchange fluid. Further, the heat exchange fluid is suppliedin fluid communication with a heat exchanger. Yet further, the heatexchanger is provided with means for sensing a fluid flow rate and meansfor sensing a temperature. Further yet, at least one of the fluid flowrate and the temperature is controllably selected by a computer.

In another related embodiment, the step of transferring the processwafer to the heating chamber is effectuated by a means for remotelymanipulating the process wafer under controlled ambient conditions.

In yet another related embodiment, the acidic residue is selected fromthe group consisting of HBr, HCl and HF.

Another aspect of the present invention provides a heating chambersystem for reducing acidic contamination on a process wafer following aplasma etching process.

These and other embodiments, aspects and features of the invention willbe better understood from a detailed description of the preferredembodiments of the invention which are further described below inconjunction with the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a typical plasma etching systemaccording to the prior art.

FIG. 2 is a schematic representation of a plasma etching system showingselected features of the present invention.

FIG. 3 is a schematic representation of a heating chamber according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method and apparatus according to the present invention is moreclearly described by referring to FIG. 2. FIG. 2 is a schematicrepresentation of a multi-chamber processing system for carrying outshallow trench isolation (STI) etching. As previously discussed withreference to. FIG. 1, several modular processing chambers may beattached to the processing system for carrying out different procedures.An exemplary system for example is the Centura 5200 ™ commerciallyavailable from Applied Materials, Inc. of Santa Clara, Calif. Themultiple chamber system has the capability to transfer a wafer betweenits chambers without breaking the vacuum and without having to exposethe wafer to moisture or other contaminants outside the multiple chambersystem. An advantage of the multiple chamber system is that differentchambers in the multiple chamber system may be used for differentpurposes in the entire process. The process may proceed uninterruptedwithin the multiple chamber system, thereby preventing contamination ofwafers that often occurs when transferring wafers between variousseparate individual chambers (not in a multiple chamber system) fordifferent parts of a process.

For example, referring to FIG. 2, in an STI process several differentetching chambers optimized for different etching steps may be used asshown, for example, at 20, 22, 24, and 26, while another chamber, forexample 28 may be used for wafer orientation, and other chambers, forexample, 30 and 32, used for loading and unloading process wafers. Inthe method and apparatus according to the present invention, a heatingchamber, 34, is added to the multi-chamber system to heat the processwafer prior to transfer by robotic arm 36 to a loadlock chamber e.g., 30or 32 for unloading. According to the present invention an external heatexchanger 38 is fluid communication by lines 39 and 40 with a heatexchange surface (see FIG. 3) disposed in chamber 34 and in contact witha process wafer for heating the process wafer.

According to the present invention, the heating chamber is used to heatthe wafer to a temperature sufficient to vaporize any condensed acidicresidue, for example HBr, remaining from the etching process on thewafer surface or on loose particles adhering to the wafer surface. Whilevaporizing of the acidic residue, a vacuum system is simultaneously usedto remove the vaporized gases from the chamber. Suitable pressures maybe maintained with a range of 10 mTorr to 500 mTorr. A suitable wafertemperature for vaporizing HBr from the wafer surface has been found tobe within a range of about 75° C. to 100° C., although most preferablythe wafer temperature is about 80° C. Further, it has been found thatthe removal of acidic contamination, for example, HBr, by heating theprocess wafer to about 80° C. can be optimally performed by, forexample, by subjecting the process wafer to heating for a period ofabout 45 to about 75 seconds, most preferably about 60 seconds withremoval of about 85% of the acidic contamination. It will be appreciatedby the skilled practitioner that the process time may be varied byaltering the pumping speed (or pressure) and/or by altering heattransfer characteristics.

According to the present invention, the process wafer is heated byconvective and conductive methods preferably by passing a heat transferfluid through a base plate equipped with a heat exchange manifold withthe base plate in contact with the process wafer. Any suitable heattransfer fluid, such as water or a glycol/water mixture may be used.Further, any suitable heat exchange manifold allowing heat transfer maybe used, however heat exchange surfaces that optimize heat transfer arepreferable and are well known in the art. For example, according to thepresent invention, a wafer support plate (base plate) used in thecooling chamber of the prior art in as shown in FIG. 1 at 24 may bemodified or replaced with a heat exchange system according to thepresent invention to allow a heat transfer fluid in communication with aheat exchanger to pass heat exchange fluid through the base plate heatexchange manifold to convectively and conductively remove heat from theprocess wafer.

According to the present invention, the heat exchanger is preferablyattached external to the process chamber and may be advantageouslyequipped with an interlock flow switch to alert the operator shouldfluid flow be interrupted. Any suitable interlock flow switches, whichare well known in the art, may be used. Further, conventional methods ofinterfacing the heat exchanger for computer control may beadvantageously used. For example, the heat exchanger may contain aconventional temperature sensor and a conventional flow rate sensor foradjusting a temperature and a flow rate, respectively. A suitable heatexchanger, for example, is preferably one that may easily maintain aflowing heat exchange fluid temperature according to the presentinvention within a range of 75° C. to 100° C.

Further, the chamber walls may additionally be fitted with heat exchangeconduits, as are well known in the art, for likewise passing a heatexchange fluid also preferably heated to about 80° C. to minimizecondensation of the acids (e.g., HBr or HCl) that have been vaporizedfrom the process wafer from re-condensing onto the walls of the heatingchamber.

Referring to FIG. 3 where the heating chamber is shown in greaterdetail, in operation, heating chamber 302 houses base plate 304 equippedwith a heat exchange manifold (not shown) and a heat exchange surface303 and the base plate is in fluidic communication with heat exchanger322 located externally to the chamber 302, the chamber ambient pressurebeing maintained under vacuum by vacuum pump 312. Heat exchange fluid issupplied by pump 309 from heat exchanger 322 by way of line 314 to baseplate 304 equipped internally with a heat exchange manifold (not shown)in contact with heat exchange surface 303 which in turn contacts wafer308 to convectively and conductively transfer heat between the heatexchange fluid and the process wafer 305, respectively. Following heattransfer to heat exchange fluid the heat exchange fluid passes by line316 to heat exchanger 322 for heat exchange and fluid temperaturecontrol.

Line 316 is equipped with an interlock flow switch 308 which is inelectronic communication by conventional wire or wireless means (e.g.,cable 311A), with controller 310. Controller 310 may also be inelectronic communication with chamber process control functions (notshown) and with heat exchanger 322 (e.g., 311B) and pump 309 (e.g.,311C) for taking desired action upon an interruption in heat exchangefluid flow, adjusting a flow rate for temperature control of the fluidor for adjusting a heat exchange rate. Controller 310 may additionallycontrol the temperature of the heat exchange fluid passing through heatexchanger 322.

According to the present invention it has been found, for example, thatHBr concentrations present on a process wafer following an etchingprocess according to the prior art were at levels of 0.3 to 0.5 ppm. Incontrast, after using the method and apparatus according to the presentinvention, HBr concentrations present on a process wafer following anetching process, for example, an STI etching process, were reduced toless than 0.05 ppm. As a result, acidic contamination levels werereduced in the loadlock chambers and wafer processing defects due tocorrosive action were likewise reduced thereby increasing overall waferprocessing throughput and semiconductor feature (e.g., STI features)quality. Moreover, the corrosive action that the etching system partshave been subjected to by acidic contamination such as the robotic armand loadlock chamber parts according to the prior art has been reducedaccording to the present invention.

The preferred embodiments, aspects, and features of the invention havingbeen described, it will be apparent to those skilled in the art thatnumerous variations, modifications, and substitutions may be madewithout departing from the spirit of the invention as disclosed andfurther claimed below.

What is claimed is:
 1. A method for reducing acidic contamination on aprocess wafer and in an unloading chamber following a plasma etchingprocess to reduce acidic residue contamination comprising the steps of:providing an ambient controlled heating chamber separate from an etchingchamber and unloading chamber for accepting transfer of a process waferunder controlled ambient conditions prior to transfer to the unloadingchamber; transferring the process wafer to the heating chamber undercontrolled ambient conditions following plasma etching of the processwafer; providing a heat exchange surface comprising a wafer supportplate within the heating chamber for heating the process wafer; heatingthe process wafer by supplying a heat exchange fluid through the wafersupport plate to heat the process wafer to vaporize acidic residueremaining on the process wafer from the plasma etching process to formacidic vapors; and, simultaneously applying a vacuum pressure to theheating chamber to remove the acidic vapors from the heating chamber. 2.The method of claim 1, wherein about 50 percent to about 100 percent ofthe acidic residue is removed.
 3. The method of claim 1, furthercomprising the step of transferring the process wafer to the unloadingchamber for unloading the process wafer.
 4. The method of claim 1,wherein the process wafer is heated within a temperature range of about75 degrees Centigrade to about 100 degrees Centigrade.
 5. The method ofclaim 4, wherein the vacuum pressure comprises about 10 milliTorr to 500milliTorr.
 6. The method of claim 5, wherein the step of heating theprocess wafer is carried out for a period of about 30 to about 90seconds.
 7. The method of claim 1, wherein the heat exchange fluid issupplied at a selected flow rate and fluid temperature by a heatexchanger.
 8. The method of claim 7, wherein at least one of the heatexchange fluid flow rate and the heat exchange fluid temperature isadjusted in response to a sensed fluid flow rate and a sensed fluidtemperature.
 9. The method of claim 1, wherein the step of transferringthe process wafer to the heating chamber is effectuated by a means forremotely manipulating the process wafer under controlled ambientconditions.
 10. The method of claim 1, wherein the acidic residue isselected from the group consisting of HBr, HCl and HF.